Other Important Reactions of Carboxylic Acids

Decarboxylation

Sodium salts of carboxylic acids undergo decarboxylation to form alkanes when distilled with soda lime (NaOH + CaO).

Hell-Volhard Zelinsky (H.V.Z)

α-substituted carboxylic acids are formed when carboxylic acids react with Cl₂ or Br₂ in the presence of red phosphorus. This reaction is known as Hell-Volhard Zelinsky reaction or in short H.V.Z reaction.

Important points regarding Hell-Volhard Zelinsky reaction

• Since formic acid (HCOOH) does not have any alkyl group, it does not undergo this reaction.
• Bromination exclusively occurs at the α-position and the reaction stops after all the α-hydrogens have been replaced by the bromine atoms. Chlorination, on the other hand, first occurs at α-position and when all the hydrogen atoms have been replaced by chlorine atoms, it occurs further along the chain.

Electrophilic Substitution Reactions in Aromatic Acids

Aromatic carboxylic acids undergo electrophilic substitution reactions such as halogenation, nitration and sulphonation. Since the -COOH group is electron-withdrawing, the substitution occurs at meta position. The -COOH group is deactivating, therefore, the reactions take place under drastic conditions.

Nitration

Sulphonation

Friedel-Carfts reactions

Benzoic acid does not undergo Friedel-Crafts reactions because -COOH group is strong electron attracting group and deactivates benzene ring for alkylation and acylation.

Conversion